The present disclosure relates to a recording apparatus which performs recording on an optical disc recording medium which has a reference plane with a position guider and a recording layer formed at a depth position different from that of the reference plane.
As an optical disc recording medium (optical disc) recording/reproducing a signal by light emission, for example, a CD (Compact Disc), a DVD (Digital Versatile Disc), and a BD (Blu-ray Disc: registered trademark) have come into wide use.
As an optical disc which is the next generation of optical discs such as a CD, a DVD, or a BD which have come into wide use, the applicant has earlier suggested a so-called bulk recording optical disc disclosed in Japanese Unexamined Patent Application Publication No. 2008-135144 and Japanese Unexamined Patent Application Publication No. 2008-176902.
Here, the bulk recording is a technique for achieving large-capacity recording by emitting a laser beam to an optical recording medium (bulk recording medium 100), which has at least a cover layer 101 and a bulk layer (recording layer) 102, while sequentially changing a focal position and performing multi-layer recording in the bulk layer 102, as shown in FIG. 25.
As for the bulk recording, Japanese Unexamined Patent recording technique called a so-called micro-hologram method.
In the micro-hologram method, a so-called hologram recording material is used as a recording material of the bulk layer 102. For example, a photo-polymerizing photopolymer is widely used as the hologram recording material.
The micro-hologram method is broadly classified into a positive type micro-hologram method and a negative type micro-hologram method.
The positive type micro-hologram method is a method of condensing two light fluxes (light fluxes A and B) facing each other to the same position and forming fine interference fringes (hologram) so that the interference fringes are configured as recording marks.
The negative type micro-hologram method is a method of erasing interference fringes formed in advance by emitting a laser beam so that the erased portions are configured as recording marks, as an opposite idea to the positive type micro-hologram method. Specifically, in the negative type micro-hologram method, an initialization process is performed to form the interference fringes in advance in the bulk layer 102 before a recording process is performed. That is, light fluxes C and D are radiated with parallel light to form the interference fringes in the entire bulk layer 102. Then, after the interference fringes are formed through the initialization process in this way, information recording is performed by forming erasure marks. Specifically, the information recording is performed with the erasure marks by emitting a laser beam in accordance with information to be recorded in a state where a focus is made at an arbitrary layer position.
The applicant has also suggested a recording method of forming voids (holes or blanks) as recording marks as a bulk recording method different from the micro-hologram method, as disclosed in Japanese Unexamined Patent Application Publication No. 2008-176902.
The void recording method is a method of emitting a laser beam with relatively high power to the bulk layer 102 made of a recording material such as a photo-polymerizing photopolymer to record holes in the bulk layer 102. As disclosed in Japanese Unexamined Patent Application Publication No. 2008-176902, the holes formed in this way become portions with a refractive index different from that of other portions in the bulk layer 102, and thus the reflectance of light can be increased in the boundary portion therebetween. Accordingly, the holes serve as the recording marks, and thus the information recording is realized by forming the hole marks.
Since the hologram is not formed by the void recording method, the recording is achieved by emitting light from one side. That is, it is not necessary to form the recording marks by condensing two light fluxes to the same position as in the positive type micro-hologram method.
In comparison to the negative type micro-hologram method, there is an advantage that the initialization process is not necessary.
Japanese Unexamined Patent Application Publication No. 2008-176902 discloses an example in which precuring light is emitted before the recording when the void recording is performed. However, the void recording can be performed even when the irradiation of the precuring light is omitted.
The bulk recording type (simply referred to as a bulk type) optical recording medium suggested in the various recording methods described above has been used. However, the recording layer (bulk layer) of the bulk optical recording medium does not have an explicit multi-layer configuration in which a plurality of reflection films is formed. That is, in the bulk layer 102, reflection films and guiding grooves of each recording layer that a general multi-layer disc has are not formed.
In the configuration of the bulk recording medium 100 shown in FIG. 25 described above, focus servo or tracking servo is not performed during the recording time at which no mark is formed.
Thus, in effect, a reflection surface (reference plane Ref) serving as a reference with guiding grooves shown in FIG. 26 is formed in the bulk recording medium 100.
Specifically, guiding grooves (position guiders) configured by pits or grooves are formed on the lower surface of the cover layer 101 and a selection reflection film 103 is formed on the guiding grooves. The bulk layer 102 is laminated on the lower layer side of the cover layer 101, where the selection reflection film 103 is formed, with an adhesive material such as UV-cured resin, which is an intermediate layer 104, interposed therebetween, as shown in the drawing.
When the medium has the above-described configuration, the bulk recording medium 100 is radiated with a servo laser beam as a position control laser beam apart from a mark recording laser beam (recording laser beam), as shown in FIG. 27.
As shown in the drawing, the bulk recording medium 100 is radiated with the recording laser beam and the servo laser beam via a common object lens.
At this time, when the servo laser beam reaches the bulk layer 102, there is a concern that the servo laser beam may have a bad influence on the mark recording in the bulk layer 102. For this reason, in a bulk recording method according to the related art, a laser beam with a wavelength range different from that of the recording laser beam is used as the servo laser beam, and the servo laser beam is reflected from the reflection film formed on a guiding groove formation surface (reference plane Ref). The selection reflection film 103 is formed which has a wavelength selection property of reflecting the servo laser beam and transmitting the recording laser beam.
Next, a process of recording marks in the bulk recording medium 100 under the above-described hypothesis will be described with reference to FIG. 27.
First, when multi-layer recording is performed on the bulk layer 102 with no guiding groove or no reflection film, the position of a layer in which marks are recorded in the depth direction of the bulk layer 102 is set in advance. FIG. 27 shows an example in which a total of five information recording layer positions L, a first information recording layer position L1 to a fifth information recording layer position L5, are set as layer positions (also referred to as mark formation layer position: information recording layer positions) at which marks are formed in the bulk layer 102. As shown in the drawing, the first information recording layer position L1 is set at a position distant by a first offset of-L1 in a focus direction (depth direction) from the selection reflection film 103 (reference plane Ref) in which the guiding grooves are formed. Further, the second information recording layer position L2, the third information recording layer position L3, the fourth information recording layer position L4, and the fifth information recording layer position L5 are set at positions distant from the reference plane Ref by a second offset of-L2, a third offset of-L3, a fourth offset of-L4, and a fifth offset of-L5, respectively.
At the recording time at which no mark is formed, the focus servo or the tracking servo may not be performed at each layer position L in the bulk layer 102 based on the reflected beam of the recording laser beam. Accordingly, focus servo control or tracking servo control of the object lens during the recording time is performed so that the spot position of the servo laser beam tracks the guiding grooves on the reference plane Ref based on the reflection light of the servo laser beam serving as a position control beam.
However, it is necessary for the recording laser beam to be allowed to reach the bulk layer 102 formed below the selection reflection film 103 to record the marks. In this case, accordingly an optical system includes a focus mechanism adjusting a focusing position of the recording laser beam apart from a focus mechanism for the object lens.
FIG. 28 is a diagram illustrating an example of the inner configuration of a recording apparatus, which includes a mechanism independently adjusting the focusing position of the recording laser beam, for the bulk recording medium 100.
In FIG. 28, a first laser diode 111 indicated by LD1 is a light source of the recording laser beam and a second laser diode 119 indicated by LD2 is a light source for the servo laser beam. As described above, the first laser diode 111 and the second laser diode 119 are configured to emit laser beams with different wavelength ranges, respectively.
As shown in the drawing, the recording laser beam emitted from the first laser diode 111 is incident, via a collimation lens 112, on a focus mechanism which includes a fixed lens 113, a movable lens 114, and a lens driving unit 115. When the lens driving unit 115 drives the movable lens 114 in a direction parallel to the optical axis of the recording laser beam, a collimation state (converged/parallel/diverged state) of the recording laser beam incident on the object lens 117 in the drawing can be changed and the focusing position of the recording laser beam can be adjusted independently from a change in the focusing position by the driving of the object lens 117.
In terms of this meaning, the focus mechanism is also referred to as a recording light focus mechanism.
The recording laser beam passing via the recording light focus mechanism is incident on a dichroic mirror 116 which is configured to transmit light with the same wavelength range as that of the recording laser beam and reflect light with other wavelength ranges.
As shown in the drawing, the bulk recording medium 100 is radiated with the recording laser beam transmitted through the dichroic mirror 116 via an object lens 117. The object lens 117 is held so as to be displaceable in the focus direction and the tracking direction by a biaxial actuator 118.
The servo laser beam emitted from the second laser diode 119 passes through a beam divider 121 via a collimation lens 120 and is incident on the above-described dichroic mirror 116. The servo laser beam is reflected from the dichroic mirror 117 and is incident on the object lens 117 so that the optical axis of the servo laser beam is identical to the optical axis of the recording laser beam passing through the dichroic mirror 116.
The servo laser beam incident on the object lens 117 is focused on the selection reflection film 103 (reference plane Ref) of the bulk recording medium 100 when the biaxial actuator 118 is driven under the focus servo control of the servo circuit 125 described below. Simultaneously, the position of the servo laser beam in the tracking direction is configured to track the guiding grooves formed in the selection reflection film 103 when the biaxial actuator 118 is driven under the tracking servo control of the servo circuit 125.
The reflected beam of the servo laser beam from the selection reflection film 103 is reflected from the dichroic mirror 116 via the object lens 117, and then is reflected from the beam divider 121. The reflection light of the servo laser beam reflected from the beam divider 121 is condensed to a detection surface of a photo detector 123 via a condensing lens 122.
A matrix circuit 124 generates each error signal of focus and tracking based on a light signal received by the photo detector 123 and supplies each error signal to the servo circuit 125.
The servo circuit 125 generates a focus servo signal and a tracking servo signal from the respective error signals. When the above-described biaxial actuator 118 is driven based on the focus servo signal and the tracking error signal, the focus servo control and the tracking servo control are realized by the object lens 117.
Here, when the marks are recorded at a necessary information recording layer position L among the information recording layer positions L set in advance in the bulk recording medium 100, the driving of the lens driving unit 115 is controlled to change the focusing position of the recording laser beam by an offset of corresponding to the selected information recording layer position L.
Specifically, the setting control of the information recording position is performed by, for example, a controller 126 which performs control of the entire recording apparatus. That is, when the controller 126 controls the driving of the lens driving unit 115 based on an offset amount of-Lx set in advance in correspondence with a target information recording layer position Lx, the information recording position (focusing position) of the recording laser beam matches the target information recording layer position Lx.
The tracking servo of the recording laser beam during the recording time is automatically performed by performing the tracking servo control of the object lens 117 based on the reflected beam of the servo laser beam by the servo circuit 125, as described above. Specifically, the spot position of the recording laser beam in the tracking direction is controlled so as to be located directly below the guiding grooves formed on the reference plane Ref.
When the bulk recording medium 100 subjected to the mark recording is reproduced, it is not necessary to control the position of the object lens 117 based on the reflected beam of the servo laser beam from the reference plane Ref, as in the recording time. That is, at the reproduction time, the focus servo control and the tracking servo control of the object lens 117 can be performed based on the reflected beam of a reproduction laser beam by emitting the reproduction laser beam to the mark lines formed at the information recording layer position L to be reproduced.
In the bulk recording method, as described above, the bulk recording medium 100 is configured to be radiated with the recording laser beam serving as the mark recording beam and the servo laser beam serving as the position control beam (which are synthesized on the same optical axis) via the common object lens 117. Further, the focus servo and the tracking servo of the recording laser beam can be performed by performing the focus servo control and the tracking servo control of the object lens 117 based on the reflected beam of the server laser beam, even when the guiding grooves or the reflection surface with the guiding grooves is not formed in the bulk layer 102.
When the above-described servo control method is adopted, there is a problem in that the information recording position is deviated in the tracking direction due to the lens shift of the object lens 117 caused by the eccentricity of the bulk recording medium 100 or the backlash of a slide mechanism or the like of an optical pickup.
Here, the lens shift caused by the backlash of the slide mechanism means that the position of the object lens 117 being subjected to the tracking servo control is shifted to absorb the displacement of the position as the position of the optical pickup is displaced abruptly (instantly) due to the occurrence of the mechanical backlash of the slide mechanism during slide servo control.
FIGS. 29A to 29C are diagrams for explaining a principle in which deviation of an information recording position is caused due to the above-described lens shift.
FIG. 29A shows an ideal state where no eccentricity of the bulk recording medium 100 or no backlash of the slide mechanism occurs and no lens shift of the object lens 117 occurs. FIG. 29B shows the lens shift (referred to as eccentricity of a + direction) occurring toward the left side of the drawing (referred to as an outer circumference direction). FIG. 29C shows the lens shift (referred to as eccentricity of a − direction) occurring toward the right side of the drawing (referred to as an inner circumference direction).
A central axis C in the drawing is a central axis set in design of the optical system. In the ideal state shown in FIG. 29A, the center of the object lens 117 is identical to the central axis c.
When the lens shift occurs in the + direction, as shown in FIG. 29B, the center of the object lens 117 is shifted in the + direction with reference to the central axis c of the optical system.
At this time, since the servo laser beam (patterned beam in the drawing) is incident as the parallel light on the object lens 117, the position of the focal position is not changed in the tracking direction in spite of the fact that the shift occurs from the central axis c of the object lens 117. On the other hand, since the recording laser beam (white beam in the drawing) is focused at the necessary information recording layer position L in the bulk layer 102 below the reference plane Ref, as described above, the recording laser beam is incident as non-parallel light on the object lens 117. Therefore, the recording laser beam is shifted with respect to the object lens 117 in the + direction, and as shown in the drawing, the focal position (information recording position) of the recording laser beam is changed by a distance corresponding to the lens shift amount in the + direction (in the drawing, by a deviation amount +d).
When the lens shift occurs in the − direction shown in FIG. 29C, the information recording position of the recording laser beam is changed by a distance corresponding to the lens shift amount in the − direction (in the drawing, by a deviation amount −d).
The problem occurs in that the information recording position of the recording laser beam 100 is deviated in the tracking direction due to the eccentricity of the disc or the backlash of the slide mechanism in the configuration of the bulk recording apparatus medium described above with reference to FIG. 28, that is, in the configuration in which the focus servo control of the object lens 117 is performed in such a manner that the recording laser beam and the servo laser beam are emitted via the common object lens 117 so that the servo laser beam is focused on the reference plane Ref of the bulk recording medium 100, in which the focal position (information recording position) of the recording laser beam is adjusted by changing the collimation state of the recording laser beam incident on the object lens 117, and in which the tracking servo control of the object lens 117 is performed so that the focal position of the servo laser beam tracks the guiding grooves formed on the reference plane Ref.
At this time, the information recording positions may overlap between the adjacent guiding grooves depending on the magnitude or the like of the eccentricity or a track pitch (formation interval of the guiding grooves). Then, a recording signal may not be reproduced appropriately.
As described above, the main cause of the deviation of the information recording position is the lens shift of the object lens 117. However, the deviation of the information recording position is likewise caused due to disc tilt.
As one countermeasure for resolving the deviation of the information recording position, there can be used a method of making the track pitch larger than a variation in the information recording position.
However, this method has a problem in that it is difficult to determine the size of the track pitch since the maximum amount of lens shift or the like is uncertain. Above all, there is a problem in that a recording capacity may be reduced due to the expansion of the track pitch.
As another countermeasure for resolving the deviation of the information recording position, there can be used a method of not making a disc detachable in a system.
Here, for example, an error between the inner diameter of the disc and the clamp diameter of a spindle motor is the cause of the eccentricity. Since it is difficult to completely eliminate the error therebetween during processing, the eccentricity is unavoidable. Further, even when the error therebetween can be completely eliminated, the center of a recording signal in the reference plane of the disc may not be identical to the center of a spindle axis of the recording apparatus. Therefore, the eccentricity also occurs in this case. Accordingly, in the system in which the disc is not detachable, it is possible to avoid the problem that the recording positions overlap with each other since the influences of the eccentricity become the same as each other. Thus, since the track pitch can close up, the recording capacity can be increased by that amount.
However, the disc may not be, of course, substituted in this method. Therefore, the disc may not be substituted, for example, when the disc becomes faulty. Further, data recorded by a recording apparatus may not be read by another recording apparatus. Thus, convenience may therefore deteriorate.
A so-called ATS (Adjacent Track Servo) method can be taken into consideration as an effective method of resolving this problem. The ATS has originally been studied as a self servo track writer (SSTW) in a hard disc drive.
FIG. 30 is a diagram illustrating the ATS.
In the ATS, as shown in the drawing, a recording spot Srec and an adjacent track servo spot Sats are formed on a recording medium. The recording spot Srec and the adjacent track servo spot Sats are formed by radiating the recording medium with a beam drawing a circle via a common object lens. At this time, the distance between these spots is configured to be fixed.
In the ATS, when the recording spot Srec serves as a preceding spot (that is, the outer circumference side when a traveling direction of recording is the inner circumference to the outer circumference) and the adjacent track servo spot Sats serves as a following spot, the tracking servo is applied on a mark line formed by the recording spot Srec serving as the preceding spot. Eventually, the tracking servo control of the object lens is performed so that the adjacent track servo spot Sats tracks an immediately previous track in which the recording spot Srec is formed.
According to the ATS, the problem of the tracks overlap each other (the information recording positions overlapping each other) due to the influence of the eccentricity or the like since the track pitch is constant as the distance between the spots S does not occur. That is, it is not necessary to enlarge the extra track pitch or to configure the disc so as not be detachable in the system in consideration of the deviation of the information recording position caused due to the eccentricity or the like, as described above.